An air-conditioning unit 100 in the related art shown in FIG. 4, commonly known as an upright-type air-conditioning unit, includes a vent opening 103 communicating with a vent outlet port 102 through which air is delivered toward the upper part of the occupant's body and a defrost opening 105 communicating with a defrost outlet port 104 through which air is directed toward the windshield F, both formed at the top of the unit case 101. In addition, a steering member support part 106 extending along the width of the vehicle (along the left/right direction relative to the vehicle body) is disposed to range across the space near the air-conditioning unit 100, and a defrost duct 108 (or a vent duct 107) so as to bypass the steering member support part 106 in the regular layout. In the air-conditioning unit 100 in the related art structured as described above, the vent opening 103 and the defrost opening 105 are normally disposed respectively on the rear side and on the front side along the frontward/rearward direction relative to the vehicle body. FIG. 5 schematically illustrates the structure of the vent duct 107 in an air-conditioning system equipped with this air-conditioning unit 100. The vent duct 107 includes two central communication passages 107a communicating with a central vent outlet port 102a present substantially at the midpoint along the width of the vehicle (along the left/right direction) within the cabin and two side communication passages 107b communicating with side vent outlet ports 102b each present at one of the two ends along the width of the vehicle inside the cabin.
The inventions disclosed in the related art in relation to automotive air-conditioning units include the following. In the automotive air-conditioning system disclosed in patent reference literature 1, central vent (central face) openings are formed at the two ends of the air-conditioning unit along the width of the vehicle and a side vent (side face) opening is formed at the center of the air-conditioning unit along the vehicle width so as to increase the flow rate with which air is let out by reducing the extent of pressure loss over the area corresponding to the central communication passages 107a mentioned earlier.
Patent reference literature 1: Japanese Unexamined Patent Publication No. 2003-326948 (see paragraphs 0010˜0012, FIGS. 1 and 7)